A. March is okay but it would be nicer if you applied fertilizer a bit earlier, say in late January or early February. Roses perform better in soils enriched with compost, applied fertilizers high in phosphorus and iron and wood mulch several inches deep.
Rosarians who want high quality roses fertilize multiple times during the year. The first fertilizer application (light) is at bud break in the spring, a second one when the flower buds have developed and not yet opened and a final one in the fall from late August through September. A number of them like fish emulsion and Epsom salts as additional feedings through the summer months when roses go into a kind of high temperature dormancy.
Use a good quality rose fertilizer such as Peters or Miracle Gro plus an application of iron chelate, preferably EDDHA, applied to the soil. If you are applying iron to the foliage you will have to wait until they fully leaf out in about March. Foliar sprays use a spreader or liquid detergent added to the spray solution at the very end of the mixing.